Effects of Higher-Rank Multipoles on Spectral Lineshapes of Higher Quadrupolar Nuclei near the Null Point in Inversion-Recovery Experiments

The effects of higher-rank multipoles on the spectral lineshape of I = 5 2 and 7 2 quadrupolar nuclei have been examined near the null point in the inversion-recovery measurements. ²⁷Al (I = 5/2) and ¹³³Cs (I = 7/2) NMR inversion-recovery experiments were performed in D₂O/glycerol-d₈ solutions. The longitudinal and transverse relaxational matrix elements using state multipole formalism for spin- 5/2, - 7/2, and - 9/2 have been derived. It is found that the null-point spectra of spin- 5/2, - 7/2, and - 9/2 are similar to those of the spin- 3/2 system. This indicates that the direct coupling between rank-one and rank-three elements plays the key role in the generation of fine structure in null-point spectra.